Barbell squats are great for increasing glute and thigh strength (and thus definition), but like any exercise the results aren't going to be instant. Perhaps switch from lighter weights and lower reps which most runners do (which is endurance focused) to more weight and less reps, (say between 5-8); and make sure you're going low enough (parallel or lower, but only if you're form is spot on) to make sure you're working your glutes when you're driving upwards.

Seeing as we're almost the same in terms of height, age, running experience and weight (11 stone, was 12 stone about 2 months ago and that weight gain was due to inactivty being injured) I might as well tell you whats worked for me, but I'm no expert.

If you're looking to lose weight, it can be as simple as easting 500kcal under your daily maintance, so you're looking somewhere around 1500-1800kcal a day depending on how active you are. Judging from what you eat, you seem to lack meat, which you would need as it contains protein (or subsistutes if you are a vegeterian). Make sure you get enough protein, about 1 gram per pound of your weight to maintain lean muscle mass as you want to lose fat, not muscle. I know it sounds vague as 'eat what you want as long as it's balanced', but thats the jist of it without being too technical. Make sure you get enough carbs (complex if possible, think wholegrains and not sugars) for energy, protein to maintain muscle, and some natural fats (40/40/20 ratio). Try to avoid processed foods and sodas too as they're don't fit in with your goals of running or weightloss. I would say avoid alchohol...but I never followed that advice when I was an undergrad!

At uni I had a George Forman grill, so cooking fresh meat such as chicken or beef was very quick (and got rid of the fat too). Stir-frys were also a stapple. And pasta, like any student, but I swapped to brown pasta. Cooking more than one portion (eg chilli, pasta bake etc.) and then keepign the rest in the fridge and the freezer is also good as if you don't have the motivation to cook one day, you don't have to reach for a frozen pizza as you've got something pre-prepared.

And seeing as you're at uni; sign up with your cross country/running club, that'll help keep you running regularly and thus help with your motivation.

Disregarding your age, and looking purely at lifting and running. It's not hindering your running, unless your recovery time is making you too sore that it eats into your running. Don't give up the squats, they're great for your quads and nothing builds your core better than squats and deadlifts (make sure you have proper form for both, and going parallel on your squats). I've been lucky enough to never have any problems with my lower back and core area while running for I focused on a 5x5 barbell strength programme before getting more into running. Resistance training should be part of your weekly routine.

I've personally given up most of the lifts, apart from squats for I was just getting too fatigued and my goals have changed as I've swtiched from strength to endurance (10-12 reps per set at a lower weight). Try looking into doing leg press as well as squats, and lunges are also good for your core/legs.

Just tailor your lifting more towards your running goals. For example, are you training for strength or endurance? Trying to build mass isn't going to help your running too much at all.

Barbell squats are good, as long as you have ok form. They work mainly on your quads, core and glutes as long as you go parallel. In fact nearly all the major babrell lifts (squats, deadlifts, OHP and power cleans) all work on your core as you use it to stabilise yourself when doing these lifts; but then again lifting may not be your thing, and can be quite tiring (I've dropped most of my lifting now, apart from squats) but irregardless squats are something that should be incorporated. Leg press can be seen as an alternative to squats, but there is nothing stopping you from doing both.

Lunges too work the core and legs so are another good exercise. In short, anything that works your legs and core (feel free to include your upper body if you want to balance it out).